Phased arrays create beamed radiation patterns in free space to allow the formation of selective communication channels. A phased array is formed by placing a plurality of antennas in a grid pattern on a planar surface where these antennas are typically spaced ½ of the wavelength of the radio frequency (RF) signal from one another. The phased array can generate radiation patterns in preferred directions by adjusting the phase and amplitude of the RF signals being applied to each of the antennas. The emitted wireless RF signals can be reinforced in particular directions and suppressed in other directions by means of these adjustments. Similarly, phased arrays can be used to enhance the reception of wireless RF signals from preferred directions of free space while suppressing wireless RF signals arriving from other directions. The incoming RF signals, after being captured by the phased array, are phase and amplitude adjusted and combined to reinforce RF signals received from desired regions of free space and suppress RF signals that were received from undesired regions of free space. The wireless beam is steered electronically to send and receive a communication channel, thereby eliminating the need to adjust the position or direction of the antennas mechanically.
A phased array requires the orchestration of the plurality of antennas forming the array to perform in unison. A corporate feed network provides the timing to the phased array by delivering identical copies of an RF signal to each of the plurality of antennas forming the phased array. A uniform placement of the plurality of antennas over a planar area defines the phased array as having a planar surface area that extends over several wavelengths of the carrier frequency of the RF signal in both of the X and Y directions. For example, a phased array with 100 antennas arranged in a square planar area would have edge dimension equal to 5 wavelengths of the RF carrier frequency in each direction.
Power amplifiers (PA), which are packaged in discrete packages or integrated circuit components, amplify a transmit signal before the signal is coupled to the antenna. The power amplifier (PA) is fabricated in a semiconductor chip. The chip is then packaged and mounted onto a printed wire board (PWB) within the system. The circuit board for the PA is a PWB includes of one or more metal sheets laminated between electrically non-conductive layers of laminate. Some metal sheets are patterned to form a wiring interconnect network that electrically connects the terminals of integrated circuit components and other discrete components together as would be depicted on a corresponding circuit schematic. Other metal sheets can be used as heat spreaders to laterally spread out the heat along the plane of the circuit board. The integrated circuit components can be packaged and soldered to one of the surfaces of the PWB or surfaced mounted to the PWB as bare die and then either wire bonded or solder bumped to that surface of the PWB.
The power amplifiers of the phased array are designed to handle signals with large peak-to-average power ratio (PAPR). Such a PA would be designed to perform linearly at the peak power ration; however, doing so causes the PA to be less power efficient when the signal has an average power ratio. The occurrence of the peak power ratio is typically an infrequent event; therefore, in order to insure that the PA operates linearly at all times, the PA ends up generating large dissipative heat losses when the signal has an average power ratio. A single PA can generate 25 W or more of heat. A phased array with 100 antennas can generate as much as 2500 W. For comparison, the PA of current base stations driving a single antenna dissipates only 100's of watts.
The antennas and the electrical components of the phased array are placed in a sealed environment to protect the antennas from the weather conditions of rain, snow, etc. However, the sealed environment that is used to protect the antennas and electrical components also prevents the removal of heat generated from the PWB where the antennas are mounted. This can case problems due to overheating of the phase array system.